Porcelain Jacket Crown

Write a short note on aluminous porcelain.
Answer:

Porcelain jacket crowns (PJC) were very brittle and fractured easily. The marginal adaptation was also quite poor.
The “Mc Lean and Hughes” developed the PJC with an alumina-reinforced core in 1965.
This crown was developed to improve the strength of earlier PJC.
Aluminous porcelain is a ceramic compound of the glass matrix phase and it contains at least by volume 35% Al₂O₃.
It is a type of core porcelain. Alumina strengthens the porcelain.
Aluminous porcelain is available as body, dentin, or gingival porcelain.
Aluminous porcelain is veneering ceramic for ceramic or metal-ceramic prostheses.

Composition of Aluminous Core:

Silica − 35%

Alumina − 53.8%

Soda − 2.8%

Potash − 4.2%

Zinc oxide − Rest

Boric oxide − 3.2

Calcium oxide − 1.12%

Zirconium oxide Rest

Types of Aluminous Core:

Core Formation of Aluminous Core:

On the prepared tooth the platinum foil is adapted on to which the core porcelain is condensed.
The platinum foil along with core porcelain placed in the furnace and fired.
After cooling the rest of the body is built up using dentine, enamel, and other porcelain.
After completion of the restoration, the foil is gently teased out and discarded.

Advantages of Aluminous Core:

Disadvantage of Aluminous Core:

Do not have sufficient strength for the posterior crown.
Functions of Alumina
As powdered alumina is added to porcelain, it provides sufficient strengthening.
Alumina is slightly soluble in low-fusing porcelain allowing for continuity of atomic bonding through the ceramic.
So interface between alumina particles and porcelain is stress-free and does not encourage crack propagation around alumina particles.

Reader Interactions